1. Field of Invention
This invention relates to a brake assembly including a hub and rotor.
2. Description of Related Art
Prior brake designs are hat rotor hubs that use a hat rotor fixed to a brake hub, or integrated rotor hubs.
Integrated rotor hubs, as the name suggests, are constructions that integrate a rotor and a hub into a single element. These integrated rotor hubs are typically manufactured by known metal manufacturing methods such as sand casting. The hub and rotor are typically integrally cast. Subsequent to casting, the integrated rotor hub must be machined. The manufacturing costs of integrated hubs are considerable, as different vehicles each require a unique integrated hub design. Therefore, separate tooling and specific machining processes are also required for each integrated hub design.
In addition to the relatively high manufacturing costs of integrated rotor hubs, are high replacement costs. For example, a worn or cracked braking surface on the rotor requires the replacement of the entire hub. Such hub replacements are costly due to high labor costs and high material costs in replacing the entire integrated hub and rotor. The replacement of an integrated rotor hub requires the re-packing or re-installation of bearing assemblies that allow the hub to rotate about a wheel shaft. The bearing re-packing or re-installation procedures are labor intensive and are occasionally poorly performed. Poorly re-packed or reinstalled bearings result in excessive wear in the hub, shaft, and bearing. Poorly re-packed or re-installed bearings also result in excessive rotor run-out.
Rotor run-out is the rotational misalignment of the rotor. Specifically, rotor run-out is the measurement of the extent to which the rotor wobbles, or deviates outside the intended plane of rotation, as the rotor rotates with the hub about the wheel shaft. Rotor run-out causes excessive and uneven wear in the rotor braking surfaces and in brake pads which contact the rotor braking surfaces. Rotor run-out also increases thermal distortion of the brake rotor. The thermal distortion results in thermal judder, noise, and vibrations during braking, as well as causing irregular braking pulsations.
Hat rotor hubs have a hat rotor that is detachable from a hub. These hat rotors are typically one piece metal castings having a rotor portion integrally cast with a hat portion. The hat portion of the hat rotor is a large flange that fits over a mounting surface of the hub. The hat portion includes wheel stud apertures through which wheel studs can pass. The hat rotor is loosely mounted on the hub until a wheel is subsequently mounted on the hub. As wheel lug nuts are tightened to the wheel studs, the hat rotor is sandwiched between the wheel and the hub, thus securing the hat rotor to the hub.
Hat rotor hubs have an advantage over integrated rotor hubs. Hat rotors can be easily replaced when the brake surfaces of the rotor become worn or cracked, or the rotor becomes warped. However, hat rotors also have deficiencies.
A deficiency with hat rotor hubs results from the configuration of the typical hat rotor hub design. Hat rotors and hubs are typically individual metal castings. Subsequent to casting, the hat rotor and the hub must both be individually machined. The machined surfaces of the rotor hat portion, the rotor braking surfaces, and the mounting surface of the hub must all be in the proper plane to minimize rotor run-out. The rotor braking surfaces extend outwardly a considerable distance from the rotor hat portion. Consequently, the rotor braking surfaces also extend outwardly a considerable distance from the mounting surface of the hub, where the rotor hat portion is mounted on the hub. Should the mounting surface of the hub, or the hat portion, include an imperfectly machined surface, the rotor will have considerable run-out as it rotates. Stated differently, a small error in the machined surfaces of the mounting surface, or the rotor hat portion, will have a proportionally magnified effect on the rotational alignment of the rotor braking surfaces due to the large distance the rotor braking surfaces extend from the mounting surface.
Another deficiency with hat rotor hubs results from the manner in which a hat rotor and a wheel are mounted together on the hub. The hat rotor is installed over a mounting surface of the hub. The hat rotor is loosely mounted on the hub until a wheel is subsequently mounted on the hub. As wheel lug nuts are tightened to the wheel studs, the hat rotor is sandwiched between the wheel and the hub, thus securing the hat rotor to the hub. However, if the wheel lug nuts are not evenly tightened, the uneven forces acting on the hub may result in the distortion of the hub. Additionally, if the wheel rim has been improperly manufactured, the wheel rim might impose a distortion on the hub as the lug nuts are tightened. Any distortion on the hub will be directly transferred to the rotor, as the portion of the hub that is potentially distorted is also the mounting surface for the rotor in all hat rotor designs.
Additionally, as the hat rotor is loosely held on the hub when the wheel is removed, debris such as brake pad material or dirt can slip between the rotor hat portion and the mounting surface when the wheel is removed from the hub. Extraneous material in this location will obviously prohibit the hat portion from mating properly with the mounting surface of the hub. Extraneous material will cause the rotor to run-out as it rotates about the wheel spindle.
Another deficiency of hat rotor hubs is the requirement of a specific hat rotor for every hub. Consequently, specific casting tooling and specific machining steps are typically required for each hat rotor hub design. The cost of hat rotors is increased as the tooling, casting, and machining costs are greatly increased due to the large number of hat rotors that must be manufactured. Inventory costs are also correspondingly increased.
FIG. 20A is a partial side view in section of a prior art hat rotor hub assembly. Specifically, FIG. 20A shows a wheel shaft 1002, a hub 1012, which rotates about the wheel shaft 1002 through bearings 1009a and 1009b, a nut 1004 securing the hub 1012 to the wheel shaft 1012, and a hat rotor 1018 that includes a hat portion 1030 and opposing braking surfaces 1040 and 1042. The hub 1012 further includes a mounting surface 1013 and a plurality of wheel studs 1015 which extend outwardly from the mounting surface 1013. The hat portion 1030 of the hat rotor 1018 includes a mounting surface 1032 which mates with the mounting surface 1013. The hat portion 1030 also includes wheel stud passages 1034 through which the wheel studs 1015 pass. A wheel (not shown) is mounted on the hub outwardly of the hat portion 1030. The wheel (not shown) would contact the exterior surface 1033 of the hat portion 1030. A wheel lug nut (not shown) is used with each wheel stud 1015 to secure the wheel to the hub. Upon the securement of the wheel to the hub, the hat portion 1030 of the hat rotor 1018 is sandwiched between the wheel and the mounting surface 1013. However, when the wheel is removed, as is shown in FIG. 20A, the hat rotor 1018 is loosely held on the hub 1012.
The mounting of the wheel on the hub and the tightening of the lug nuts both may contribute to rotor run-out in this hub design. Both the rotor and the wheel are mounted at the same location on the hub (the mounting surface 1013). Should the mounting surface become distorted, the rotor will subsequently also become distorted. Unevenly tightened lug nuts may distort the mounting surface 1013. An improperly manufactured wheel rim (not shown) also could distort the hub mounting surface 1013, as the rim is tightened onto the hub.
FIG. 20A also shows the rotor braking surfaces 1040 and 1042 of the hat rotor 1018 are disposed at a considerable distance from the mounting surface 1013 on the hub 1012. Consequently, the rotor brake surfaces 1040 and 1042, the hat portion mounting surface 1032, and the mounting surface 1032 need to be properly machined so that the rotor braking surfaces 1040 and 1042 rotate in planes that are perpendicular to the rotational axis of the hub xe2x80x9cAxe2x80x9d with minimum run-out. Clearly, due to the considerable distance of the rotor braking surfaces from the mounting surface, a small error in any of the machined surfaces of the mounting surface, or the rotor hat portion, will have a proportionally magnified effect on the rotational alignment of the rotor braking surfaces causing run-out.
FIG. 20B is a partial side view in section of a prior art integral rotor hub assembly. Specifically, FIG. 20B shows a wheel shaft 1102, a hub 1112, which rotates about the wheel shaft 1102 through bearings 1109a and 1109b, a nut 1104 securing the hub 1112 to the wheel shaft 1112, and rotor 1118 that includes opposing braking surfaces 1140 and 1142. The rotor 1118 is integrally manufactured with the hub 1112, and is attached to the hub through the connecting element 1114. The hub 1112 further includes a wheel mounting surface 1113 and a plurality of wheel studs 1115 which extend outwardly from the wheel mounting surface 1113. A wheel (not shown) is mounted on the hub on the wheel mounting surface 1113. A wheel lug nut (not shown) is used with each wheel stud 1015 to secure the wheel to the hub.
Another deficiency of both integrated rotor hubs and hat rotor hubs is that the rotor in both of these designs is fixed with respect to the hub. Consequently, the rotor must be carefully balanced to avoid uneven wear and compromised performance. During braking, the rotor in such an assembly is subjected to high frictional forces that generate heat in the rotor causing thermal expansion/distortion, temperature variation across the face of the rotor, and heat transfer to the adjacent components including the hub and the bearings. Heat transferred to the bearings will cause distortions reducing the bearing performance. Bearing grease will also break down more rapidly under high heat situations.
When the rotor is fixed with respect to the hub, thermal expansion of the rotor is very limited because of the integral connection between the rotor and the hub. This creates thermal coning in the rotor surface and a large thermal gradient, which will induce high thermal stress leading to thermal cracking. The high thermal gradient generated during braking and the effects of the thermal expansion and distortion can cause vibration and thermal judder across the brake surfaces, resulting in a rough or irregular braking pulsations. The high thermal stress and thermal distortion also reduce the life and performance of the rotor and increase maintenance costs.
Particularly in high performance and commercial braking applications, braking performance is especially stringent and closely monitored. It is important in such applications to provide a braking assembly that provides enhanced performance at low maintenance and replacement costs.
One aspect of embodiments of the invention is to provide a braking assembly that is suitable for use on commercial vehicles, especially highway vehicles with a gross vehicle weight (GVW) of 5000 pounds or more and high performance vehicles.
Another aspect of embodiments of the invention is to provide a rotor that can be manufactured separately from a hub and which may be easily removed from the hub for replacement. Lower maintenance costs can be realized by this invention by allowing replacement of the rotor without a hub change. This eliminates the disturbance of wheel bearings, as well as the labor intensive replacement or re-packing of wheel bearings.
Another aspect of embodiments of the invention is to provide a hub and rotor where the rotor mounts to the hub independent of the wheel. Specifically, an aspect of embodiments of the invention is to provide a hub having a rotor mounting flange and a rotor which is mounted to a rotor mounting flange. The independent mounting of the rotor and a wheel to the hub rotor assembly of the present invention ensures that the rotor run-out will be unlikely to result from unevenly tightened lug nuts or an improperly manufactured wheel.
Also as a result of the independent mounting of the rotor and the wheel, wheel removal does not affect the mounting of the rotor to the hub. Consequently, upon removal of the wheel from the hub there is no potential for debris or other extraneous matter to become lodged between the rotor and the hub, causing rotor run-out.
Another aspect of embodiments of the invention is to provide a rotor design having simplified manufacturing compared to hat rotor hubs and integral rotor hubs. Specifically, an aspect of embodiments of the invention is to provide a hub having a rotor mounting flange and a rotor, which is mounted to the rotor mounting flange. This hub and rotor configuration provides a rotor that is as easily removable from the hub as a hat rotor, but does not have the deficiencies of a hat rotor. And, as there is no hat portion on the rotor, different rotors do not vary considerably in shape from one another. Consequently, unlike hat rotors and integral rotor hubs, a large number of rotors may be machined from a single rough casting. Tooling and manufacturing costs are greatly decreased as a result of this design. Additionally, as the rotor and the hub are manufactured separately, the hub and rotor can have different material specifications for optimal cost and performance.
Another aspect of embodiments of the invention is that the rotor is not integrated with the hub and, therefore, heat generated on the rotor during braking is not transferred directly to the hub and the bearings, resulting in reduced bearing performance.
Another aspect of embodiments of the invention is that the rotor and hub of the invention may be designed to use a variety of different fasteners for attachment of the rotor to the hub.
Another aspect of embodiments of the invention is to provide a rotor that floats with respect to the hub. An additional aspect of these embodiments of the invention is to reduce first and second order thermal distortion by allowing the rotor to thermally expand. Embodiments of the invention provide a design that significantly reduces the temperature variation and thermal distortion across the rotor surface. This design can reduce thermal fatigue and prolong the life of the rotor.
Another aspect of embodiments of the invention is to use a floatation element with each fastener to allow the rotor to float or move with respect to the hub. The element can be made of a material resistant to corrosion and having low thermal conductivity so as to be viable for commercial highway vehicles. The invention can reduce vibration and thermal judder across brake surfaces to ensure a smooth pedal feel during automobile or other vehicle braking applications.
A further aspect of embodiments of the invention is to provide a spring clip spacer in association with the flotation element. The spring clip spacer allows floatation of the rotor to occur relative to the hub, which eliminates rattling noises.
Another aspect of embodiments of the invention is that the spring clip spacer can serve as a heat shield between the rotor and the hub. The spring clip spacer may be manufactured from such metals as stainless steel that have low heat conductivity. Consequently, heat generated in the rotor is less likely to be transferred to the hub and the bearings.
Another aspect of embodiments of the invention is that the spring clip spacer may be manufactured from metals such as stainless steel that minimize the potential for corrosion. The spring clip spacer separates the floatation element from the hub rotor mounting flange slot within which it is disposed and minimizes any corrosion, galvanic corrosion, galling, etc. that might occur on or between the floatation element and slot. Such corrosion, galling etc. can eliminate rotor floatation or diminish the performance of the rotor floatation. This feature is of particular significance in road vehicles as opposed to race vehicles, as a rotor may remain mounted on a hub of a road vehicle without disassembly for a number of years, race vehicles typically have each mechanical component removed for inspection following each race. Consequently there is little chance of corrosion or galling to occur. Additionally, road vehicles, are subject to road salt and other chemicals, which accelerate corrosion considerably.
Another aspect of embodiments of the invention is that the spring clip spacer minimizes the Brinell effect of the floatation element of the hub rotor-mounting flange. The floatation element is typically constructed from corrosion resistant alloys having a hardness considerably higher than the hub, which is typically constructed from aluminum or an aluminum alloy. As the floatation element floats within the slots of the hub rotor-mounting flange, the harder floatation element dents and scores the slot. This Brinell effect type of denting and scoring alters the clearances between the floatation element and the slot, thus altering the floatation of the rotor. The spring clip of the present invention separates the floatation element from the slot and prohibits the floatation element from contact with the slot. Consequently, no Brinell effect denting or scoring of the slot will occur. This feature is also of significant importance in road vehicles where the rotor may remain attached to the hub for considerable periods of time. The cumulative effect of Brinell effect denting and scoring over a long period of time may result in significant deterioration within the slots of the hub rotor mounting flange. Such Brinell effect denting and scoring are problematic in race vehicles, as well. However, the frequent inspections and parts replacements that are common place in race vehicles diminishes the cumulative effect of Brinell effect denting and scoring.
Another aspect of embodiments of the invention is that the spring clip spacer provides protection to the hub in situations where the floatation element is manufactured from a metal which is harder than a metal used to manufacture the hub. The spring clip spacer assists in the provision of floatation to the rotor, but minimizes the potentially damaging contact the harder floatation element can impart on the hub. Accordingly, there is little chance that the hub slots within which the floatation elements and the spring clip spacers are disposed will increase in size as a result of the floatation.
These and other aspects and advantages of the invention can be realized by the various embodiments of the hub rotor assembly of the invention. Other objects, aspects, and advantages of the embodiments of the invention will become apparent from the detailed description taken in conjunction with the drawings.